The images of the Watergate scandal have become part of our nation's collective memory: Richard Nixon flashing his trademark victory sign before boarding a helicopter to leave the White House after resigning in disgrace is just part of the scrapbook.
Nixon announced his resignation on Aug. 8, 1974, more than two years after the break-in at the Watergate complex offices of the Democratic National Committee during the 1972 campaign. By then, questions about Nixon's involvement in the Watergate break-in were coming from all directions.
"What did the president know, and when did he know it?" Republican Sen. Howard Baker demanded at the height of the investigation.
Today, on the 30th anniversary of the infamous break-in, the mysteries surrounding the event that led to the resignation of an American president are every bit as tantalizing.
After all the hearings, all the headlines and all the cover-up, we still don't know whether Nixon actually knew about the break-in in advance.
But another mystery might be cracked much sooner: that 18½-minute gap in one of Nixon's infamous tape recordings at the White House
"We have decided that the time is right and appropriate to determine whether that conversation can be retrieved or recovered," said Karl Weissenbach, a Nixon tape archivist at the National Archives. The tapes were last examined in 1974. But since then, the technology used to decipher recordings has improved dramatically.
The 18½ minutes in question is part of Nixon tape 342, recorded on June 20, 1972, three days after the Watergate break-in. On the tape, Nixon discussed the incident for the first time with his chief of staff, H.R. Haldeman. It is unknown whether the tape was deliberately or inadvertently erased for those 18½ minutes.
Amid the Watergate scandal, Nixon's loyal secretary, Rose Mary Woods, said she erased the tape while reaching for a phone call. Reporters were calling it the "Rose Mary Stretch." Back then, it was assumed that the 18½ minutes was gone forever, but technology may provide a surprise footnote to history.
"You never completely erase a tape," said Stephen St. Croix, a forensic audio expert with Intelligent Devices, near Washington, D.C. "You think you do, but you really don't."
St. Croix, a former musician, does most of his work for law enforcement, and like other forensic audio experts, he uses computers to help decipher old tapes, old recordings, or intercepted communications in which it seems impossible to understand what is being said.
The technology also allows for the retrieval of sound that has been erased, where the speech cannot be heard at all.
The key to such work is to find the scraps of sound left on the tape that can be made into audible voices, and removing everything else.
"It would take a human hours to find them," St. Croix said. "But a computer can find them in seconds."
The information comes in as analog data, from tapes, telephone or wire intercepts, and is converted to digital data in the computer. To decipher that data, forensic experts would use "bandpass filters" and other high-tech devices that look for frequencies that they do not need within a sound. It then throws them away, leaving just the frequencies of the human voices. Computers can also remove background noise.
St. Croix demonstrated how computers might be used to intercept the cell phone calls of suspected criminals.
"What we've got here is a case where a drug deal is going down and there are cell phones used that are encrypted with tones," St. Croix said. "So that if we intercept, all we hear is the screaming tones."
But with some technical intervention, which included removing the screaming tones, voices were audible on the same tape. With the voices made clear, police have evidence that may be used in court.
The National Archives, desperate to fill in the legendary gap before the Nixon tapes disintegrate, is auditioning experts, including St. Croix, for the job.
Candidates got an erased test tape to show off their skills. If any of the techs are given the original Nixon tape, the National Archives wants to make sure that they will not damage the tape, as it is a historical artifact.
In the meantime, experts including St. Croix believe they can get Nixon's voice back.
"There's always a holy grail," St. Croix said. "So in forensic audio historical recovery, this is it."
Historians wonder what on earth Nixon was trying to hide, since all the other tapes were already so damning, with blatant evidence of a cover-up.
"I have no idea, but it must have been extremely embarrassing," said Ben Bradlee, who was editor at The Washington Post when reporters Bob Woodward and Carl Bernstein broke the story. He is now Vice President at Large at the paper.
Then, there's Deep Throat, the shadowy source so dramatically portrayed in All the President's Men, a movie about how Woodward and Bernstein's investigation into the Watergate scandal set the stage for Nixon's eventual resignation.
Today, other than Deep Throat himself, only three people — Woodward, Bernstein and Bradlee — know the identity of Deep Throat. Former Nixon White House counsel John Dean claims to know, and was set to publish his latest theory today on Salon.com. But his publisher is scrambling to re-work Dean's online book, after his suspected Deep Throat denied it.
Just working in the Nixon White House made people candidates for being the secret source. ABCNEWS' own Diane Sawyer, who held several positions in the Nixon administration, was on the list, until the reporters made it clear that Deep Throat is a man.
Woodward and Bernstein have said the mystery source is not Alexander Haig, who was Deputy National Security Advisor during Watergate. But through the years, the reporters have steadfastly declined to reveal who Deep Throat is when names have been put before them.
"You know none of the three of us, Bob myself or Ben Bradlee, have gotten into the guessing game," Bernstein said.
But plenty of others have. Dean has now named three different Deep Throats, and all have denied being the one.
Bradlee says that eventually, that one day, we will all know this Watergate secret. "Sure you're going to," Bradlee said. "Woodward has said that they would reveal Deep Throat's identity when he dies."
Ultimately, the most profound Watergate puzzle may be Nixon himself. He was handily set to win re-election, yet so plagued by insecurity that he became a criminal.
"The thing that baffles me most of all is what was in Richard Nixon's brain," presidential historian Michael Beschloss said.
"Here was a man who was totally unsuited for the presidency of the United States," Bernstein added. "I think that's where the great mystery lies. How did this person get to be who he was?"